Transform "They complete the project by Friday" into future perfect tense.

The correct transformation into the future perfect tense is "They will have completed the project by Friday." This construction indicates that the action of completing the project will be finished before a specified time in the future—Friday in this case. The future perfect tense is formed by using "will have" followed by the past participle of the verb, which in this example is "completed."

In contrast, the other options either do not use the future perfect tense or misrepresent the timing and aspect of the action. For instance, the option stating "They will complete the project by Friday" uses the simple future tense, which signifies that the action will occur in the future but does not emphasize that the project will be completed by that time. Similarly, other options describe actions that are either in process, or suggest a passive construction that lacks the necessary indication of completion by Friday. Thus, the chosen answer accurately fulfills the requirement of the question by clearly conveying the intended meaning of the future perfect tense.